An increasing number of light fixtures utilize LEDs as light sources due to their lower energy consumption, smaller size, improved robustness, and longer operational lifetime relative to conventional filament-based light sources. LEDs have a distribution in optical and electrical characteristics, for example forward voltage, correlated color temperature (CCT), and light output power, which may result in undesirable visible variations in color or intensity within a luminaire using multiple LEDs, or between multiple luminaires. Such variations have been minimized in several ways. One way is the selective use of only some LEDs within a manufacturing distribution (i.e., only LEDs having characteristics falling into a specific narrow range), but the disadvantage of this approach is significantly higher cost. Another method is to provide a mixing chamber or diffusing system that mixes or homogenizes the light. This approach has two disadvantages. First, mixing systems or diffusers require additional volume within the luminaire, increasing the size and cost of the system. Second, such systems typically have increased optical losses in the mixer or diffuser, resulting in reduced efficiency.
Lighting and illumination systems that include LEDs may also suffer from the angularly dependent color non-uniformity of LEDs. In order to mitigate poor angular color uniformity, such illumination systems often require additional elements, such as diffusers, mixing chambers, or the like, to homogenize the color characteristics. Such homogenization often degrades the light-intensity distribution pattern, however, resulting in the need for secondary optics to re-establish the desired light-intensity distribution pattern. The addition of these elements typically requires undesirable additional space or volume, adds cost and expense, and reduces output efficiency.
These limitations related to LED color uniformity are particularly troublesome for luminaires having multiple light-emitting surfaces. For example, some luminaires incorporate both direct and indirect illumination, and these luminaires require separate circuit boards for each illumination direction, with each circuit board requiring a specific set of LEDs to achieve the desired color uniformity and angular color uniformity. These requirements increase the cost and complexity of such systems. Additionally, the multiple boards and necessary interconnection points may decrease reliability. As the number of emitting surfaces or emission directions increases, the cost and complexity of such lighting systems may increase significantly.
Accordingly, there is a need for structures, systems, and procedures enabling LED-based illumination systems to produce uniform color distribution of light in multiple directions and operate with high efficiency while maintaining low cost and relatively small size.